1. Field of the Invention
The present invention relates to a dental assist appliance for guiding movement of an orthodontic wire for correcting malocclusion (irregularities of teeth or an improper dental arch) and to an orthodontic appliance using it.
2. Description of the Prior Art
In general, for correcting irregularities of the teeth or an improper dental arch of anterior cross-bite (mandibular protrusion), a method in which a force is exerted on front teeth of the upper jaw so that the front teeth of the upper jaw can be moved toward the front of the front teeth of the lower jaw is typically used. Some typical examples of the method are given below.
An orthodontic wire having a diameter of about 0.5 mm, which is called an accessory spring, is brought into contact with a neck portion (a boundary between a tooth and a gum) of each tooth to be corrected at the back side (at the tongue side) so that the each tooth can be pushed forwards by the resilient force, to correct the irregularities or improper dental arch of the front teeth (Lingual Arch Method).
An elastic orthodontic wire, after fit-in from the lip side of the teeth with spaced therefrom, is fixed at its opposite ends to both molar teeth of the upper jaw with fittings. Then, the orthodontic wire is deflected to the surface of each of the front teeth to be corrected at the lip side of the teeth and is ligatured thereto. The ligatured front teeth are each retracted toward the tongue side by the resilience of the elastic orthodontic wire, to correct the irregularities or improper dental arch of the front teeth (Utility Arch Method).
A detachable inclined plane, formed in accordance with irregularities of the teeth or improper dental arch, is bitten, and the resulting force is exerted on the front teeth to be corrected, to correct the irregularities or improper dental arch of the front teeth (Inclined Plane Method).
By the aid of resilience of a pair of rubbers mounted on a headgear, a pad at one's chin is retracted backwards, to suppress the growth of the chin, to correct the irregularities or improper dental arch of the teeth (Chin Cap Method).
As shown in FIG. 6, an orthodontic wire 9, which is slidably fitted at its opposite ends to fixings 8, 8 fixed to molars 3, 3, is so secured as to extend along teeth at the lip side of the upper jaw.
The orthodontic wire 9 is ligatured (fixed) to brackets 50 bonded to front teeth 4 to be corrected. Coiled springs 91, 91 are fitted around portions of the orthodontic wire 9 extending between the fixings 8 for the orthodontic wire 9 and the brackets 50. The coiled springs 91, 91 at right and left sides, each of which is restricted at one end thereof by the fixing 8, allow the orthodontic wire 9 and the front teeth 4 ligatured thereto to be pushed forwards, to correct the irregularities or improper dental arch of the teeth.
However, the conventional methods mentioned above have the following disadvantages:
The method has the disadvantage that as the tip ends of the teeth are shifted forwards, an angle at which the accessory spring fitted to the teeth at the tongue side contacts with the surfaces of the teeth decreases, and as a result, the elastic aiding wire slips on the tooth surface at the tongue side to reduce or lose the effect.
The method using the deflection of the orthodontic wire has the disadvantage that the force exerting on the front teeth is weaken soon. For all that, if the force exerting on the front teeth is increased by increasing the degree of deflection of the orthodontic wire or by replacing it with a stronger resilient one, that arises a possible problem that the wire may contact with the lip or gum to cause an ulcer, or an excessive force may be exerted on the teeth to cause pain.
The method has the disadvantage that the inclined plane must be bitten with a weak force for long hours to take effect.
The method does not work quickly and may possibly cause a jaw-joint disorder during a long time, depending on a magnitude of force.
The method has the disadvantage that a portion of the pushing force from the coiled spring does not work in the direction for the front teeth to be shifted forwards, but acts in the direction for the front teeth to be retracted inside (median), with the result that satisfactory orthodontics cannot be achieved or it takes long tome till the completion of the orthodontics.
Further, these five methods above have the common disadvantage that the medical appliance must be attached for long hours to take effect.